Various medical procedures require the making of electrical contact with specified regions within the heart. For example, in an intra-cardial ECG (electrocardiogram), an apparatus, such as a catheter or probe, is inserted through a vein or an artery into the appropriate location within the heart. The apparatus has one or more electrodes which are placed in close proximity to the tissue of the heart so that the electrical activity within the heart can be appropriately monitored. Intra-cardial ECG sensing can be done, for example, when the apparatus is within the heart for other purposes.
Similarly, temporary pacing of the heart also requires the making of electrical contact between one or more electrodes of an apparatus, such as a probe or catheter, and the tissue of the heart. For example, during certain surgery, a catheter may be inserted into the heart to monitor various cardiovascular functions. Such a catheter may be equipped with appropriate pacing electrodes so that, if the patient should suffer a cardiac arrest, the heart can be quickly given the necessary electrical therapy.
It is conventional practice to mount the electrodes on the exterior surface of the probe or catheter, and constructions of this type are shown, for example, in Blake et al U.S. Pat. No. 3,995,623 and Khalil U.S. Pat. No. 4,217,910. Unfortunately, there is a danger that electrodes mounted on the exterior of the probe or catheter may become loose and slide off the probe or catheter and remain in the patient. This can occur, for example, as the result of sliding of the catheter through a tubular introducer which is used in placement of the catheter. In addition, an electrode mounted on the exterior surface of the probe or catheter tends to project radially beyond the catheter body line and, as such, is more likely to be slid off of the catheter as a result of relative movement between the catheter and the introducer.